Currently,
methane is transformed into methanol through the two-step
syngas process, which requires high temperatures and centralized production.
While the slightly exothermic direct partial oxidation of methane
to methanol would be preferable, no such process has been established
despite over a century of research. Generally, this failure has been
attributed to both the high barriers required to activate methane
as well as the higher activity of the CH bonds in methanol compared
to those in methane. However, a precise and general quantification
of the limitations of catalytic direct methane to methanol has yet
to be established. Herein, we present a simple kinetic model to explain
the selectivity–conversion trade-off that hampers continuous
partial oxidation of methane to methanol. For the same kinetic model,
we apply two distinct methods, (1) using ab initio calculations and
(2) fitting to a large experimental database, to fully define the
model parameters. We find that both methods yield strikingly similar
results, namely, that the selectivity of methane to methanol in a
direct, continuous process can be fully described by the methane conversion,
the temperature, and a catalyst-independent difference in methane
and methanol activation free energies, Δ<i>G</i><sup>a</sup>, which is dictated by the relative reactivity of the C–H
bonds in methane and methanol. Stemming from this analysis, we suggest
several design strategies for increasing methanol yields under the
constraint of constant Δ<i>G</i><sup>a</sup>. These
strategies include (1) “collectors”, materials with
strong methanol adsorption potential that can help to lower the partial
pressure of methanol in the gas phase, (2) aqueous reaction conditions,
and/or (3) diffusion-limited systems. By using this simple model to
successfully rationalize a representative library of experimental
studies from the diverse fields of heterogeneous, homogeneous, biological,
and gas-phase methane to methanol catalysis, we underscore the idea
that continuous methane to methanol is generally limited and provide
a framework for understanding and evaluating new catalysts and processes
